反相液相色谱法(RPLC)测定食品中维生素B_6(呲哆胺、呲哆醛、吡哆醇)

应用HPLC反相色谱法对维生素B_6(VB_6)的三种不同同系物(吡哆醇、吡哆胺、吡哆醛)进行分离测定是一种新的VB_6测定法,经充分粉碎的样品,用0.1M硫酸溶液,在120℃下水解30分钟,冷却后经离心、过滤,用ODS-C_(18)反相柱、pH2.0～2.5的硫酸溶液作流动相,在1.0ml/min的流速下,能将吡哆胺、呲哆醛、吡哆醇完全分离,并在激发波长293nm,发射波长395nm时,应用外标法定量,其回收率在99～103％,变异系数在5.0％～5.3％。实验结果表明,HPLC反相色谱法测定VB_6(吡哆胺、吡哆醛、吡哆醇)是一种快速,简便、灵敏度高,重现性好的方法。     

Effects of tetrahydroisoquinolines on dopa decarboxylase and pyridoxal kinase

The mechanism of the nullification of the therapeutic effects of levodopa by pyridoxine in parkinsonian patients is not known and is still a subject of much speculation. Among other suggestions, it has been proposed that pyridoxine and levodopa may form tetrahydroisoquinoline derivatives in vivo, which may in turn inhibit dopa decarboxylase or act as a false transmitter. This possibility was tested by synthesizing six tetrahydroisoquinoline derivatives and by studying their effects on dopa decarboxylase in brain homogenates. These compounds in concentrations of 50 mM did not inhibit dopa decarboxylase or pyridoxal kinase, which synthesizes pyridoxal phosphate.     

METOCLOPRAMIDE AS A DOPAMINE ANTAGONIST IN THE HEART AND GUT OF THE MOLLUSC TAPES WATLINGI

SUMMARY 1. Metoclopramide is a potent antagonist of the inhibitory response to dopamine in two isolated tissues, the electrically stimulated intestine and the spontaneous beating heart, from the mollusc Tapes watlingi.
2. Blockade by metoclopramide of dopamine receptors in the central nervous system of man may account for the relapse of patients with Parkinson's disease which occurs when metoclopramide is given during successful therapy with levodopa.     

Vitamin B6 deficiency: a potential cause of refractory seizures in adults

Objective: In children, vitamin B₆ (pyridoxine) deficiency has been described as a cause of seizures that are refractory to conventional antiepileptic medications. We describe the clinical presentation of 3 adults with refractory seizures (later diagnosed with vitamin B₆ deficiency) that resolved after pyridoxine treatment. Design: Case series. Setting: Tertiary care surgical intensive care unit. Patients: In the first case, a 54‐year‐old male with history of alcoholic cirrhosis developed new‐onset seizures refractory to phenytoin and levetiracetam 8 days after liver transplantation. In the second case, a 59‐year‐old male with hepatitis C infection developed intracranial hemorrhage and new‐onset seizures refractory to phenytoin, levetiracetam, and pentobarbital. The third patient is a 78‐year‐old male with a history of alcohol dependence who was admitted for an intraventricular bleed and developed new onset of refractory seizures. Interventions: Intravenous pyridoxine followed by oral pyridoxine. Measurement and Main Results: In all 3 cases, seizures persisted despite escalation of conventional antiepileptic medications but resolved within 2 days of pyridoxine supplementation. In each case, low serum pyridoxal 5′‐phosphate concentrations normalized with pyroxidine administration. Conclusions: Although refractory seizures caused by vitamin B₆ deficiency are rare in adults, it should be considered in critically ill adult patients with refractory seizures.     

The Function Of A Vitamin B6 Coenzyme In The Activation And Nuclear Binding Of Steroid Receptors

Pyridoxal 5'-phosphate reacts with activated cytosolic steroid-receptor complex, presumably by Schiff-base linkage, to inhibit its binding to DNA or cell nuclei. Vitamin B ₆ deficiency produces liver cytosol that has more activated glucocorticoid-receptor complex that can bind to DNA, and a more rapid rate of nuclear binding than controls.     

VITAMIN B6 DEFICIENCY IN RATS AND THE METABOLISM OF O-PHOSPHORYLETHANOLAMINE

Rats reared on a high-protein, pyridoxine-free diet showed osteoporotic bone changes in the tail and limb girdles, with an accompanying loss of O-phosphorylethanolamine (OPE) phospholyase activity of the liver and increased urinary excretion of OPE. It is suggested that OPE may influence bone metabolism by inhibiting alkaline phosphatase or by complexing with calcium ions. Administration of OPE was shown to increase urinary excretion of calcium.     

PHOSPHORYLASE RESPONSE TO VITAMIN B6 FEEDING

Weanling rats fed pyridoxine at levels equal to and ten times those recommended by the National Research Council accumulate extra muscle phosphorylase for at least six weeks, with reference to both age and muscle weight, but in proportion to the vitamin B₆ retained.     

Tolfenamic acid and caffeine: A useful combination in migraine

Tolfenamic acid is a potent inhibitor of prostaglandin biosynthesis, which has been proved effective in the treatment of acute migraine attacks. The usefulness of caffeine, metoclopramide and pyridoxine as adjuncts to tolfenamic acid was tested in acute migraine attacks in ten patients. A combination of tolfenamic acid (200 mg) with either caffeine (100 mg), metoclopramide (10 mg) or pyridoxine (300 mg) was given twice to each patient in random order. Thus 60 attacks were treated. The tolfenamic acid-caffeine combination proved the most effective as judged by duration and intensity of attacks, working ability, vigilance, and overall evaluation of the drugs by the patients. Metoclopramide was somewhat better than pyridoxine as an additive.     

Vitamin and homocysteine status of mothers and infants and the risk of nonsyndromic orofacial clefts

OBJECTIVE: This study was undertaken to investigate the involvement of maternal and infant B vitamins and homocysteine as risk factors for orofacial clefting. STUDY DESIGN: Venous blood samples were taken from 96 infants with nonsyndromic orofacial clefts and 88 infants without a congenital malformation and from their mothers at approximately 14 months after the index pregnancy. Red blood cell and serum folate, serum vitamin B(12), whole blood vitamin B(6) as pyridoxal-5'-phosphate (PLP), and plasma homocysteine concentrations were measured. RESULTS: A vitamin B(12) concentration of 185 pmol/L or less and a PLP concentration of 44 nmol/L or less in mothers increased the risk of having a child with an orofacial cleft (odds ratio [OR]=3.1; 95% CI: 1.3-7.4, OR=2.9; 95% CI: 1.2-7.1, respectively). Infants with orofacial clefts had a 15% lower serum folate concentration compared with controls (P=.06). CONCLUSION: A low vitamin B(12) and PLP concentration in mothers increased the risk of orofacial clefts in the offspring. A possible role of the infant's folate status is suggested.     

Maternal dietary B vitamin intake,other than folate,and the association with orofacial cleft in the offspring

Summary.Background: Periconceptional folic acid supplementation is suggested to prevent orofacial clefts (OFCs). Other B vitamins however may be beneficial as well.Aim of the study: To investigate the maternal periconceptional dietary intake of thiamine, riboflavin, niacin, pyridoxine and cobalamin in association with the occurrence of OFC.Methods: Two hundred and six mothers of a child with nonsyndromic OFC and 203 control mothers filled out a general questionnaire and a food frequency questionnaire around 14 months postpartum as a proxy for periconceptional intake. After exclusion of known pregnant and lactating mothers, those who reported to have altered their diet compared to the periconceptional period, and mothers with incidental folic acid supplement use periconceptionally, data of 182 OFC mothers and 173 controls were analysed. After logarithmic transformation, geometric means (P5-P95) were calculated and compared between the groups. After subsequent adjustment for energy, quintiles of dietary B vitamin intake were created.Results: The periconceptional intake of thiamine, niacin and pyridoxine was significantly lower in mothers of an OFC child. A trend towards risk reduction for OFC with increasing dietary intake was demonstrated for thiamine (p = 0.04) and pyridoxine (p = 0.03). Risk reductions were only demonstrated in women using folic acid supplements periconceptionally. Supplement users tended to consume a diet richer in B vitamins.Conclusions: Periconceptional intake of thiamine, niacin and pyridoxine seems to contribute to the prevention of OFC.Grant: Royal Netherlands Academy of Arts and Sciences (KNAW) Amsterdam, The Netherlands, 1997